Prime Minister John Key could be called to give evidence in an independent inquiry into the Sky City convention centre for pokies deal, after the Office of the Auditor General today said ministers could be called.

The Auditor General last week announced it would investigate the Government's decision to chose Sky City over other bidders to build a national convention centre in central Auckland.

The Government has offered legislative changes which could allow the casino to have hundreds more pokie machines in return for Sky City building the $350m centre.

Key was involved in the deal as tourism minister and said last week he had no concerns about the inquiry and would hand over any documents.

Deputy Auditor General Phillippa Smith today told Parliament's finance and expenditure select committee the office had only begun scoping work on what would be a complex inquiry.

"When we have isolated what the issues are exactly and who needs to be interviewed, then if it includes ministers, then yes ministers."

The Auditor General has recently agreed to undertake four new inquiries on ACC, Labour MP Shane Jones' decision to grant citizenship to Chinese millionaire Yong Min Yan - also known as Bill Liu - the Sky City convention centre and the Kaipara District Council's development of the Mangawhai Community Wastewater Scheme.

Auditor General Lyn Provost told the committee the four new inquiries required expertise which was putting financial pressure on the office.

"We are employing some QC's, we are employing some expert auditors. I can assure you that if I cannot do those jobs I will be coming back to Parliament to say the resources are inadequate or I do have the ability to charge for inquiries."

The Ministry of Economic Development would be the agency liable to pay for the costs of the inquiry.

However, Smith said the office had considered it and the ministry would not be charged.

Provost said the inquiries would take two to three months, except for the Kaipara District Council inquiry which was likely to take longer.

The Auditor General's Office did not have a view on whether the Government should sign a deal with Sky City while the inquiry was underway, if after more than a year of negotiation it reaches agreement with the casino.